Undefined symbols while linking OSMalloc.h using clang on OS X - c

Question

Hello and thank you for your assistance.
I'm attempting to create a simple 'hello world' using only low-level OS X kernel calls to allocate memory and write out to stdout. Why? I'm finishing up chapter 8 of 2nd Edition K&R which is focused on writing standard file library from scratch. It is, of course, totally out of date but the concept of the chapter remains. Anyway, I cannot seem to figure out how to properly link to get everything to work out and are thus earning myself lots of nice undefined symbol errors.
I have parsed through many other questions causing the same error, but have not found any that address how to link in the kernel library I'm attempting to use. The crazy long path in the third #include was needed to just get the thing to compile even prior to the link errors.
The Code:
#include <fcntl.h>
#include <unistd.h> // equivalent to (K&R) #include "syscalls.h"
#include </Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/System/Library/Frameworks/Kernel.framework/Versions/A/Headers/libkern/OSMalloc.h> // for low-level memory allocation
#define MINSTDIOTAG "com.apple.minstdio" // Used by OSMalloc from <libkern/OSMalloc.h>
#define PAGE_SIZE_64K (64 * 1024) // Page size to allocate
int main(void) {
char *base = NULL; // Memory buffer
char *ptr = base; // Location in buffer
// Create tag
OSMallocTag mytag = OSMalloc_Tagalloc(MINSTDIOTAG, OSMT_DEFAULT);
// Attempt to allocate PAGE_SIZE_64K of memory
if ((base = (char *)OSMalloc(PAGE_SIZE_64K, mytag)) == NULL)
return 1;
ptr = base;
// Stuff the buffer with stuff
*ptr++ = 'f';
*ptr++ = 'o';
*ptr++ = 'o';
*ptr++ = '\n';
*ptr = '\0';
// Write it out to stdout
(void)write(STDOUT_FILENO, base, (size_t)(ptr - base));
// Free allocated memory
OSFree(base, PAGE_SIZE_64K, mytag);
// Get out of Dodge City, Kansas
return 0;
}
Makefile:
BIN = ../../bin
ODIR = obj
CC = cc
CFLAGS = -std=c99 -Wall -g -I.
_OBJ = minstdio3.o
_BIN = minstdio3
OBJ = $(patsubst %,$(ODIR)/%,$(_OBJ))
.PHONY: all clean
all: $(_BIN)
clean:
rm -rv $(ODIR) $(_BIN)
minstdio3: $(ODIR)/minstdio3.o
$(CC) $(CFLAGS) $^ -o $#
cp -v $# $(BIN)/$#
$(ODIR)/%.o: %.c $(DEPS)
mkdir -pv $(ODIR)
$(CC) $(CFLAGS) -c -o $# $<
Errors Received:
Todds-MBP-2:cbasics todddecker$ make
mkdir -pv obj
cc -std=c99 -Wall -g -I. -c -o obj/minstdio3.o minstdio3.c
cc -std=c99 -Wall -g -I. obj/minstdio3.o -o minstdio3
Undefined symbols for architecture x86_64:
"_OSFree", referenced from:
_main in minstdio3.o
"_OSMalloc", referenced from:
_main in minstdio3.o
"_OSMalloc_Tagalloc", referenced from:
_main in minstdio3.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [minstdio3] Error 1
-- EDITS --
"Why are you not using the sbrk system call if you want low-level? This would match your use of write and shouldn't give any linking issues." (from CRD)
Using 'sbrk' (and it's cousin 'brk') was the original path I was headed down; however, the man page for 'sbrk' states, "The brk and sbrk functions are historical curiosities left over from earlier days before the advent of virtual memory management." This statement put me on a path toward trying to discover its replacement. 'malloc' is, of course, the correct and normal utility for memory allocation. However, K&R Chapter 8 is all about writing your own from base OS system calls. So, the base call I was able to find for OS X Darwin is 'OSMalloc' which I'm trying to use.

Answer 1

OSMalloc is only available for writing the kernel itself (kernel extensions, device drivers). User programs have to use sbrk.